Factors Affecting Gluten Production And Its Rheological Characterizations

Abstract

In this thesis, focus was given upon three factors affecting gluten production and
development during dough mixing namely mixing time, salt levels and water levels.
Gluten production was examined in terms of quantity and quality of gluten.
Quantity of gluten was measured in terms of wet and dry gluten content. Wet gluten
content was determined by weighing the gluten obtained from the dough washed
under running tap water. The wet gluten was dried using air oven drying method to
obtain dry gluten content. The quality of gluten was determined from the analysis of
volume expansion, extensibility and rheological characterization. The volume
expansion analysis was performed by frying the wet gluten in hot oil at 170
o
C in
deep fryer for 15 minutes. The volume of fried gluten was measured using mustard
seed displacement method and the difference between the volume of fried gluten and
the volume of wet gluten is measured as volume expansion of gluten.The main problem encountered in performing gluten and dough extensibility test is
to hold the sample so that it does not break at the jaws that hold the sample. Thus it
is one of the objectives in this study to build a simple set-up of tensile test to
determine gluten extensibility, which is one of the most common measurements
employed in determining the quality of gluten. A simple set-up of tensile test which
is attached to Instron 5566 has been build to determine gluten extensibility. Gluten
strip of about 10 mm x 10 mm x 70 mm was clamped at two ends using plastic clips
and extended at the centre by hook at speed of 300 mm min
-1
. Extensibility
parameters such as original gluten length, gluten length at fracture, measured force,
actual force acting on the gluten strips, strain and stress were obtained using the
formulas derived from the results of tensile test. The tensile test set-up was
successful in terms of providing the gluten extensibility measurements and also the
gluten did not fracture at the clamping area. Rheological characteristics of gluten, K
and n, were obtained by fitting stress-strain curve following an exponential equation,
e
s
= Ken . Two types of flour, strong and weak, were used as a comparison.
Correlation between two analyses measurements of the gluten quantity and quality
are determined at the end of this thesis.
An adequate polynomial equation model which fits the data was produced from
Design Expert V.6.0.4. P-value, R
2 and lack-of-fit value were determined to verify
the fitness of the polynomial model equation to the actual data and thus can be used
as a good prediction of the data. The results from Design Expert were then
transferred to Microsoft Excel file where the graph of the response was plotted
against the three factors studied.Results suggested that from the three factors studied, salt gave the most significant
effect (0.0001 < P < 0.02) on the gluten quantity and quality. As salt level increases,
it decreases the wet and dry gluten content. The volume expansion of gluten and the
extensibility seem to decrease with increasing salt level. This indicates that gluten
network strength reduces and it does not mix into elastic dough as salt level
increases. The next significant factor was water level (0.0001 < P < 0.67). Mixing
time was the least significant factor among the three (0.0001 < P < 0.95). For all
factors studied, the results for strong flour were higher than the weak flour in the
quantity, volume expansion and also extensibility. This demonstrates that the
quality of gluten is affected by the protein content of the flour. All correlations
between two analyses of quantity and quality measurements show positive
coefficient of correlation (R). Strong correlation between (i) gluten quantity and
volume expansion (R > 0.75), (ii) gluten quantity and extensibility (R > 0.80) and
(iii) volume expansion and extensibility of gluten (R > 0.60) were obtained for
strong flour compared to weak flour (R > 0.45; R > 0.50; R > 0.30, respectively).
These results indicate that the quality of gluten is influenced by the protein content
of the flour and the extensibility and volume expansion of gluten is positively
correlated. These correlations could be used in the food industry to improve the
gluten quantity and quality in the future.